Cucumbers Reefsafe?

[High tide]

I lost nearly everything one time when a seemingly sand dwelling cucumber crawled up the glass and was sucked into a powerhead. I had, (and still have, in it's own isolated tank), the cuc for a few years before it decided to "flirt with danger". It had happened before with another cuc but it was small and it just closed my corals up for a few days, I may have lost one or two colonies. But then I decided to try it again....never again I tell you.